This summary consists of the following 3 sections. First, an explanation of the biomechanics of concussion and repeat HAE (head acceleration events), and how the current brain injury assessment criteria has been developed through our existing understanding. Followed by a description into the different research formats being used to increase the understanding of brain injury in the world of sport/neuroscience. And finally, the future of brain injury analysis and how HIT is assisting science in furthering its understanding.
There are 3 different types of contact that produce a HAE: direct from direct head contact, indirect from body contact, and voluntary from voluntary movement, each producing different levels of impact on the brain. The baseline force of HAE changes between studies due to many uncontrolled factors including small sample sizes producing a reduced amount of data, therefore effecting comparison studies and relationship formation.
The brain is particularly hard to research due to its mechanical complexity when related to other major organs in the body, but also due to its location and the effect this has on its movement. It is also stated that structural differences in the central nervous system are present between different genders and should be recognised when analysing brain injury research, but past experiments have commonly used male participants, again effecting conclusions due to lack of data.
Linear accelerations, produced due to linear motion, increase the pressure within the area of impact and reduce the pressure in the opposite area of the brain, producing a focused impact point. This mechanism was originally used to study brain injury patterns and in the development of the first brain injury criterions.
With increased research into concussion, it was found that the injury is not only produced from a localised, focused force, but is commonly a result of distributed forces across the brain produced due to rotational accelerations, playing a significant role in concussions, especially in sports.
The 3 most common methods of applying a force to an object include tension, compression, and shear. Shear forces work perpendicular to the direction of extension. Strain is a parameter used to describe the changes in length due to an applied force. Within the brain, shear strain is shown to take place after rotational acceleration, generating a spread of forces throughout the brain and causing the distortion to brain tissue. This finding impacted the brain injury criteria we use considerably, and rotational accelerations became the primary effector whilst studying concussion mechanics.
An additional important factor that has been theorised when producing current brain injury criterions is the relationship between the frequency of head accelerations/impacts and brain injury, although certainty is reduced due to the lack of available data.
Current studies into the biomechanics of head acceleration exposures involve different formats including quantitative video analysis, multibody simulations, finite element (FE) brain models, anthropomorphic test device reconstruction, and wearable head sensors.
These approaches can be split into 2 categories: reconstruction and real-time data analysis.
Reconstruction techniques include quantitative video analysis, multibody simulators, ATD, and FE brain models. Quantitative video analysis and multibody simulators use models or videos to analyse the impact and estimate the impact with different movements, whilst ATD uses dummies with sensors attached to measure impact in different situations. These methods have related error due to many factors including not receiving real-time data directly from humans.
3D models from MRI imaging of the brain are produced in FE analysis and are used to model the different effects impact can have on the brain tissue and relate this to brain abnormalities/changes to tissue. These models are highly dependant on their modelling factors/software development and more information is required about the material properties of the brain before accurate comparisons can be made to the human brain. Modelling also is an expensive and long process, in both producing and running the models depending on their complexity. Whilst this data relies on MRI imaging from humans directly, assumptions are made about the material properties of the brain that effect the results greatly.
Sensors used to measure changes in motion include accelerometers, which measure the relative change in velocity of an individual over time, and gyroscopes, which measure the change in direction of an object.
Instrumented mouthguards have sensor embedded into the material and are being utilised to analyse brain impact. The devices have different levels of error due to noise created my movement in the mouth e.g., biting. As the technology is also custom, the device is expensive and there are issues surrounding fit due to no fitting criteria across companies, effecting the recorded data and the end-user cost.
HIT is a wearable head accelerometer sensor, measuring the change in velocity of its wearer over time and relating this to the impact force produced. Unlike others on the market, it is affordable, versatile, and easy to use, collecting and storing information essential for the user understanding the effect of their activities on their brain’s exposure to impact.
The Future of Brain Injury Criteria
There is a limitation in the study of concussion due to the brain’s complexity, and as society’s understanding of technology advances, so does our understanding of concussion.
Brain injury criteria has developed considerably over the years due to an increase in the standard and access to technology relevant to HAE in sport environments. This paper concludes that the understanding of concussion and brain related injury is lacking due to reduced evidence/ data collection during real-time activities. Previous experiments have lacked a measurement of forces over time, therefore effecting research into different factors like impact frequency, duration, location, direction, and size. There has also been reduced sample sizes and a lack in different ages and genders being involved in experiments. These issues are mainly due inaccessibility.
HIT provides an opportunity to resolve this issue as an affordable and accessible device available to the public. It is easy to use, and stores data about these impacts along with symptom questions. This data can be used to anonymously identify activities and forces that cause brain injury symptoms and thus, provide more information about sports impact on the brain. This will protect sport participants and add knowledge to side-line reviewing of concussive symptoms without effecting the sport, and it can also help provide data to form different relationships between brain injury and factors including gender and developed neurological diagnoses.